1. Field of the Invention
The present invention relates to an image exposure apparatus in which an image is exposed onto a photosensitive material based on image data in such a manner that main scan and sub-scan are effected for the photosensitive material by a light source unit.
2. Description of the Related Art
Currently, a number of image exposure apparatuses each having a digital exposure system mounted thereon have been developed. Generally, in the digital exposure system, an image is recorded on a recording medium in such a manner that a light beam outputted from a semiconductor laser is modulated with image data and deflected by the high-speed rotation of a polygon mirror (main scan), and the light beam reflected by the polygon mirror is further subjected to sub-scanning by a galvano mirror or the like, or the above main scan is effected repeatedly while the recording medium is moved (or the recording medium is moved stepwise). Here, as the recording medium, a photosensitive drum electrified by corona discharge, or a photosensitive material may be used. Further, in place of the semiconductor laser, another light emitter such as a light emitting diode (LED) may be used as a light source.
In the above-described image exposure apparatus, it is necessary that the starting point of each main scanning line is aligned in the sub-scanning direction. For this reason, a sensor (which will be generally referred to as an SOS sensor) is provided within a widthwise range of main scan and at a position other than an image recording region, and at a predetermined time after light at the time of main scan is detected by the SOS sensor, an image data signal is outputted. As a result, the time when output of an image signal starts at each main scan becomes constant and distortion of an image, and the like can be prevented accordingly.
However, when the SOS sensor is used for the synchronization as described above, the time of detection by the sensor may not become constant. Namely, a detection surface of the sensor has a certain region, and the signal is not reversed unless a predetermined amount of light is detected in the certain region. For this reason, the time of the image signal outputted may change due to inconsistency of the reverse timing.